Photozincography

This method enabled the accurate reproduction of images, manuscript text and outline engravings, which proved invaluable when originally used to create maps during the Ordnance Survey of Great Britain during the 1850s, carried out by the government's Topographical Department, headed by Colonel Sir Henry James.

[1] The foundation of this method is the insolubility of bichromate of potash upon exposure to light, allowing the printing of images onto zinc from photographic negatives.

At this time, high-contrast negatives were made using the wet plate collodion method (a solution of nitrocellulose in ether or acetone on glass).

Once the negative had been made, a sheet of thin tracing paper was coated in a mixture of saturated potassium bichromate solution and gum water, and dried.

The bichromate/gum mixture remained soluble on the parts of the tracing paper that were shielded from light by the opaque areas of the negative, allowing it to be removed, leaving an insoluble ‘positive’ image.

John Walter Osborne (1828–1902) developed a similar process and for the same reasons as Sir Henry, to avoid using the tracing system of the pantagraph.

After reading it, he said at once it was the same process, and I then told him it was useless for him to attempt to take out a patent as my printed Report had everywhere been circulated[5] Sir Henry, despite being the person who oversaw and set up the photography department, was not the actual inventor.